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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        /*
        封装一个函数 sendAJAX 发送 GET AJAX请求
        参数 URL
        返回结果 Promise 对象;
        */
        function sendAJAX(url){
            return new Promise((resolve, reject)=>{
                const xhr = new XMLHttpRequest();
                xhr.open('GET',url);
                xhr.send();
                //处理结果
                xhr.onreadystatechange = function(){
                    if(xhr.readyState === 4){
                        //判断成功
                        if(xhr.status>= 200 && xhr.status < 300){
                            resolve(xhr.response);
                        }else{
                            reject(xhr.status);
                        }
                    }
                }
            })
        }

        sendAJAX('https://api.apiopen.top/getJoke').then(
            value=>{
            console.log(value.response);
            },reason=>{
                console.log(reason);
        })

    </script>
</body>
</html>